window 7 home edition

Did the computer come with Windows 7 or did you upgrade from Vista? In either case, try using the built-in Factory Restore.

Windows Vista: Dell Factory Image Restore
1 Turn on the computer. When the Dell logo appears, press <F8> several
times to access the Vista Advanced Boot Options window.
2 Select Repair Your Computer.
The System Recovery Options window appears.
3 Select a keyboard layout and click Next.
4 To access the recovery options, log on as a local user. To access the
command prompt, type administrator in the User name field, then
click OK.
5 Click Dell Factory Image Restore.
NOTE: Depending upon your configuration, you may need to select Dell
Factory Tools, then Dell Factory Image Restore.
The Dell Factory Image Restore welcome screen appears.
6 Click Next.
The Confirm Data Deletion screen appears.
NOTICE: If you do not want to proceed with Factory Image Restore, click Cancel.
7 Click the check box to confirm that you want to continue reformatting the
hard drive and restoring the system software to the factory condition, and
then click Next.
The restore process begins and may take five or more minutes to complete.
A message appears when the operating system and factory-installed
applications have been restored to factory condition.
8 Click Finish to reboot the system.

If this restore Vista, that's okay. You can then use your Windows 7 disc to upgrade from Vista to Windows 7. All you need is the installation key.